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This invention relates to apparatus for measuring ligamentous insufficiency in the knee to enable a physician to provide a diagnosis of injury or abnormal operation for evaluation of different treatment methods. In the past, abnormal motion between the tibia and the femur was detected by a physician by manipulation of the leg by hand. Often the motion of a leg with a ligament tear is subtle and difficult to quantify or even compare with the patient's uninjured leg. Because a normal knee may have a substantial motion, it is desirable to quantitatively measure the displacement to allow an accurate comparison between the patient's normal and injured knees to determine the extent of injury. Further, it is desirable to quantify such measurements to compare motion of the patient's knee with statistical norms or with past records to monitor the progress of treatment.
While an electromechanical instrument has been devised for measuring the anterior drawer in the legs of normal volunteers and patients with known anterior cruciate deficits in a clinical research study, the device has certain disadvantages. The instrument is expensive and bulky and is not autoclavable to allow for its use in the operating room. Further, the instrument cannot measure knee motions of the knee when the patient is standing or walking.
The apparatus of this invention is autoclavable and is designed for use in both the 20.degree. anterior draw and 90.degree. anterior draw tests and without refitting is designed for use in measuring posterior excursions. It is believed that measurement of both anterior and posterior excursions provides the physician with the maximum useful data for proper diagnosis and treatment.
The first of such instruments utilized a modified dental chair and measurements of knee laxity were obtained by measuring motion relative to the chair. This required that the patient's leg be immobilized at various points to assure accuracy of the measurements. Improved devices, such as that disclosed in our U.S. Pat. No. 4,534,364, issued Aug. 13, 1985, entitled, "Sagittal Knee Test Apparatus," provide exoskeletal frame structures that permit comparative measurements to be taken from the light weight frame structure itself, thus freeing the patient from the chair and improving the accuracy of measurements. Such apparatus was nevertheless designed for operation while a patient was seated, preferably with an adjustable support device for the lower legs as described in the cited reference. While the improved device described was mechanical in operation, other devices for anterior/posterior laxity measurement have utilized electronic, leg mounted measuring means in conjunction with leg supports of various types.
In addition to anterior/posterior laxity measurement, it is advantageous to measure varus-valgus laxity and axial rotation of the tibia relative to the femur. These additional measurements greatly enhance the ability to correctly determine the severity of injury and in particular whether it is the anterior cruciate ligament, medial collateral ligament or both that are damaged.
In designing equipment for measuring knee laxities it is desirable to have the measuring framework connect to the body at long skeletal prominences with minimal restriction of normal joint motions. The framework must therefore be light in weight and mechanically self-contained without mechanical connection to external structures. Preferably, the exoskeletal structure should permit ambulatory motion to allow measurements to be obtained during normal movement such as walking as well as during conventional, contrived examination procedures. Although such an ambulatory exoskeletal framework has been experimentally constructed for hip motions including tibial rotations, heretofore such a structure adapted to measure anterior/posterior and varus-valgus laxities as well as tibial rotation has not been devised. The dynamic sagittal knee testor of this invention is designed to perform the standard knee laxity tests at various measured flexion angles of the lower leg and uniquely generate laxity measurements while walking.